Aftermarket SMT

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  • dmsolomon
    Handtools only
    • Jan 2015
    • 2

    Aftermarket SMT

    Greetings all,

    New to the forum and a quick (probably too quick) of a search didn't yield what I was really looking for. So, I thought I'd make a new post.

    I have a BT3100 that I've owned for about 10 years, but probably haven't used in about 4 or 5. Still works great, except for the Sliding Miter Table. It simply doesn't slide. Apparently years of being in sub-zero Minnesota temps in my garage resulted in brittle plastic slides that cracked and are no longer working.

    I took a look online and bought new plastic parts for the slide only to find out that one was missing. In fact, the missing one is no longer made. It's the bottom plastic slide (Part #661844, or Slide "A").

    I called Ryobi and, sure enough, they don't make it anymore.

    Now I'm either at a point where I'm looking for a workaround. I'm not sure I want to build anything, but is there an aftermarket sliding fence that people have found success with?

    Thanks in advance,

    David
  • Black wallnut
    cycling to health
    • Jan 2003
    • 4715
    • Ellensburg, Wa, USA.
    • BT3k 1999

    #2
    Moved to discussions. I would think the parts are available somewhere. I've not heard of any aftermarket SMT that has been adapted to the BT3K saws however there are aftermarket SMT's available for other saws. If you paired that with whatever rail system the other saws use I could see it working nicely. Cost wise it likely would not be worth it.
    Donate to my Tour de Cure


    marK in WA and Ryobi Fanatic Association State President ©

    Head servant of the forum

    ©

    Comment

    • poolhound
      Veteran Member
      • Mar 2006
      • 3195
      • Phoenix, AZ
      • BT3100

      #3
      Welcome David,

      I converted to using sleds for cross cuts and miters but I do have the dual miter slot table. These can sometimes still be found online or occasionally you can find a member here who has a spare or is parting out an unused saw. I find them easier and more accurate than the SMT.

      If you are looking for parts and can send me a pic of what you are looking for I may have something. I have a box of odd BT parts and as I don't use the SMT anymore I wouldn't have a problem parting with them (pun intended)

      I also have at least one maybe two old compete SMTs (no fence) somewhere but not sure if they are 3000 or 3100s. Not sure I want to cannibalize them but if you want a whole unit let me know and I will go look.
      Jon

      Phoenix AZ - It's a dry heat
      ________________________________

      We all make mistakes and I should know I've made enough of them
      techzibits.com

      Comment

      • Black wallnut
        cycling to health
        • Jan 2003
        • 4715
        • Ellensburg, Wa, USA.
        • BT3k 1999

        #4
        I'd be rather nervous about that vendor as well. The website just does not give me good vibes.
        Donate to my Tour de Cure


        marK in WA and Ryobi Fanatic Association State President ©

        Head servant of the forum

        ©

        Comment

        • jdon
          Established Member
          • Feb 2010
          • 401
          • Snoqualmie, Wash.
          • BT3100

          #5
          Would this be an application for a 3D printer?

          Comment

          • Neal
            Established Member
            • Apr 2012
            • 181
            • Williamstown, WV (Mid Ohio Valley)
            • Ryobi BT3000

            #6
            Look on Ebay.

            http://www.ebay.com/itm/Ryobi-BT3100...16.m2518.l4276 This one is currently $35

            http://www.ebay.com/itm/RYOBI-BT3000...p2056016.l4276This one is $75.

            Comment

            • mmcmac
              Forum Newbie
              • Nov 2014
              • 53

              #7
              Originally posted by dmsolomon
              I have a BT3100 that I've owned for about 10 years, but probably haven't used in about 4 or 5. Still works great, except for the Sliding Miter Table. It simply doesn't slide. Apparently years of being in sub-zero Minnesota temps in my garage resulted in brittle plastic slides that cracked and are no longer working.
              Are you the original owner of the saw? I have a bt3000 cabinet shop refugee which arrived with cracked slides. However this appears due to the former owner excessively torquing the eccentric screws presumably to "tighten up" the SMT ways resulting in stress failure of the slides. The OEM slides appear to be injection molded delrin/acetal, which for reference has a service temperature range of -40*C~80*C.

              The design of the SMT slide bearings is rather perplexing. The only motivation for the nested two-part configuration appears to be a concession to injection mold simplicity. Otherwise a single piece design would be functionally equivalent at the cost of a more complex mold or resorting to machining the bearing from a blank.

              In any event it is fairly straightforward to fabricate a replacement bearing from an acetal/delrin block. A square cut 22.25mm per side with a thickness of 7.5mm and center drilled at 8mm dia can be fabricated with woodworking tools. A 0.1" sawn kerf 3/16" deep spaced 0.108" from the bearing top is then cut around the circumference. The only semi critical dimension is the 0.108" kerf setback from the bearing top (upper) surface which establishes the elevation of the SMT relative to the saw work table.

              The 7.5mm block thickness is just a convenience as the eccentric screw is intended to seat at approximately this depth in the block. Likely half-inch delrin will be used to fabricate the bearing and can be used at its full thickness if the eccentric screw is countersunk such that it seats at a 7.5mm net thickness. Countersinking can be accomplished immediately after drilling the 8mm bolt hole, via a 1/2" straight router bit using the drill press quill to carefully route out the countersink. Doing so creates a greater perpendicular bearing surface reducing the frequency of re-snugging the bearings agaist the ways. Also a uniformly square bearing provides four orientations which doubles the consumable wear surfaces relative to the OEM design.

              Attached are measurements of the OEM block I'd captured some time ago when discussing this issue. Delrin/acetal can be found in small quantities from Enco, evilbay, etc. It is also possible to experiment with cast off PE or PP cutting boards although these materials will not produce a bearing with the durability of acetal.
              Attached Files
              Last edited by mmcmac; 01-23-2015, 06:16 PM. Reason: Add detail.

              Comment

              • Black wallnut
                cycling to health
                • Jan 2003
                • 4715
                • Ellensburg, Wa, USA.
                • BT3k 1999

                #8
                @mmcmac Thank you for this post confirming what I know but did not have the memory to articulate. The part abut the material properties and suitability to the purpose.

                My thought was to use a very hard hard wood to mill replacements should mine ever wear out, which they have not. I have not even had to turn mine around. I keep my base waxed and clean. I treat the SMT as the precision instrument that it is.
                Donate to my Tour de Cure


                marK in WA and Ryobi Fanatic Association State President ©

                Head servant of the forum

                ©

                Comment

                • mmcmac
                  Forum Newbie
                  • Nov 2014
                  • 53

                  #9
                  Originally posted by I saw that!
                  It shouldn't be too difficult to ditch the slides altogether in favor of a scheme using readily available, inexpensive, generic parts.

                  1. double-sealed miniature ball bearings
                  I spent a fair amount of time tossing around approaches for using miniature ball bearings for SMT bearing retrofit. It is possible even to the extent the eccentric screw alignment mechanism could be retained for its original purpose. However the clearances are rather tight and wipers would be needed on the bearings/ways to avoid sawdust entrapment between the rolling bearing and Al way. In contrast the acetal bearings are inherently self wiping

                  Same goes for the rip fence. Those slides are very rare and costly now. It'd be a simple mod to install pins in the front block for the bearing axles.
                  I have a saw with an aftermarket Excalibur fence designed exactly as such using ball bearing rollers in the fence head. It works fine until sawdust gets clumped up in the front wheel grooves after which the movement is erratic due to the entrapped debris. Worse yet due to the extremely low friction of the underlying ball bearings the fence is difficult to position as even minute debris deflects the fence during lockdown to either side of the debris location. In this case a linear slide acetal bearing both inherently clears the mating way of sawdust and provides just enough friction to keep the fence put during lockdown. Using a more positive locating mechanism other than one's hand (threaded rod, etc..) will overcome the lack of friction in some scenarios but isn't a universal solution.

                  I just pulled a bearing (#16 slide) from a rip fence and it appears equally straightforward to fabricate from a 1/2" x 1" acetal bar. I also checked Enco and found a 24" bar for $11.30 here. Enco frequently runs free shipping promotions.

                  3. metal rod with Delrin or nylon sleeves
                  This would likely be the simplest scenario for creation of replacement bearings. However the rod retrofit will need some thought as intermediate rod braces will be needed to keep static and dynamic (vibration) deflection to reasonable tolerances. This would then require the acetal bearings be cut to clear the rod supports.

                  At this point we're nearing full circle back to the original design which is inherintly ridgid for the designed service and unless the Al ways become bent or gouged, is arguably the best compromise given the relative ease an acetal replacement bearing can be fabricated.
                  Last edited by mmcmac; 01-26-2015, 08:25 AM. Reason: clarity

                  Comment

                  • capncarl
                    Veteran Member
                    • Jan 2007
                    • 3564
                    • Leesburg Georgia USA
                    • SawStop CTS

                    #10
                    Why not make the slides out of hardwood? It won't last forever but will probably last as long as the drive belts!
                    capncarl

                    Comment

                    • mmcmac
                      Forum Newbie
                      • Nov 2014
                      • 53

                      #11
                      Originally posted by I saw that!
                      Modded nylon brushes attached to the head, maybe? It could be made to not look too ghetto.
                      Felt would probably give better coverage vs. a brush and be less permeable to dust intrusion. But it may take some thought to achieve a full dust seal around the aperature of a rotating bearing.

                      I disagree. The idea behind my post was to use only off-the-shelf parts, requiring only simple cuts for length, simple holes drilled for mounting and minor grinding of certain areas of the SMT.
                      Creation of a replacement SMT bearing block for the OEM design from a acetal blank should involve no more tooling than a tablesaw, drill press, and measurement caliper.

                      I think with sufficiently sturdy material (and large enough diameter), the rod shouldn't flex under normal circumstances, so I'm not convinced that the proposed intermediate braces would be necessary. The rods aren't really that long, after all.
                      The miter base (#14) is roughly 36" long and the largest ground steel drill rod which may fit is 0.5" OD. Assuming the rod is supported at both ends it can be modeled as a simple beam with the deflection resulting from a representative 5lb loading at mid point being calculated via:

                      I = pi/4 * r^4 = 3.07e-3 [effectively a measure of beam cross-sectional stiffness]
                      E = 29e6 lb/in^2 [for steel, material elasticity]
                      y = Px^3 / (48EI) = 5.0 * 36 ^ 3 / (48 * 29e6 * 3.07e-3) = 0.055" [y-axis deflection]

                      or a bit over 1/20". If two rods are used the above deflection will be halved but vary linearally with force applied. The 5lb loading is just an example and rather optimistic given this force would be easily exceeded in practice. Breaking the 36" span in half via an intermediate support at 18" will reduce deflection by a factor of 8. Two intermediate evenly spaced supports will increase stiffness by 27x.

                      Ryobi deemed the rod type a cost-effective solution for their RTS31.
                      From the RTS31 parts manual the sliding bar (#56) appears to have a considerably wider x-axis cross section compared to a 0.5" diameter steel rod. As above the section stiffness [I] increases exponentially with an increase in section width. So given the clearance constraints between the miter table top (#1) and miter base (#14) increasing the x-axis rail cross section greatly reduces deflection of the SMT along the arbor axis. This is likely the motivation for the wide miter base (#14) as given the x-axis cross sectional width chosen in the existing design, deflection parallel to the blade is insignificant.
                      Last edited by mmcmac; 01-25-2015, 05:54 PM. Reason: clarity.

                      Comment

                      • mmcmac
                        Forum Newbie
                        • Nov 2014
                        • 53

                        #12
                        Originally posted by capncarl
                        Why not make the slides out of hardwood? It won't last forever but will probably last as long as the drive belts!
                        Uniform isotropic materials such as the plastics discussed have greater tensile strength and would likely be easier to machine to the needed tolerances. But in a pinch I don't see a problem with using a dense hardwood assuming the grain is oriented parallel to the table. Even doing so the risk of bearing fracture is greater in the event the SMT is lifted resulting in tension across the grain.

                        In any case after machining the wood I'd probably drop in into hot paraffin for a few minutes to saturate the wood acting as a lubricant and render it more resistant to dimensional change due to moisture content variation.
                        Last edited by mmcmac; 01-25-2015, 06:11 PM. Reason: clarity.

                        Comment

                        • Neal
                          Established Member
                          • Apr 2012
                          • 181
                          • Williamstown, WV (Mid Ohio Valley)
                          • Ryobi BT3000

                          #13
                          Another from Ebay...



                          Just started and ends in about a week.

                          FWIW.

                          Comment

                          • capncarl
                            Veteran Member
                            • Jan 2007
                            • 3564
                            • Leesburg Georgia USA
                            • SawStop CTS

                            #14
                            I've built several table saw sleds that I incorporated drawer slides for the Y axis instead of miter slots. If not fully extended the heavy duty slides are pretty accurate, and you can use a gang of them. You might try them om the SMT.

                            Comment

                            • dmsolomon
                              Handtools only
                              • Jan 2015
                              • 2

                              #15
                              Wow

                              Wow...

                              Tons of responses.

                              Thank you all. I figured I'd get an e-mail or something when there was a response, but never got anything so I figured there weren't any. Then I logged in today and saw all of the great info.

                              Over the weekend, I did some looking and saw the Sears Craftsman branded version of the table saw (or maybe just similar) that seemed to have the part available.



                              So, I ordered a few. We'll see how it goes.

                              Comment

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